1. Field of the Invention
This invention relates to a curable resin composition which, in a multilayer printed circuit board having conductor circuit layers and insulating layers alternately built up or superposed on a substrate, is capable of forming insulating layers excelling in adhesiveness with conductor layers and also excelling in resistance to heat, a multilayer printed circuit board manufactured by using the curable resin composition, and a method for the production thereof.
2. Description of the Prior Art
For the production of a multilayer printed circuit board, a method which comprises laminating a plurality of circuit boards having a prescribed circuit pattern formed in advance thereon through the medium of prepregs as adhesive insulating layers, pressing the laminate thus obtained, drilling and making plated through-holes to interconnect the circuits in the component layers has been heretofore known to the art (lamination pressing method). The lamination pressing method, however, necessitates use of production facilities which are very voluminous and highly expensive and incurs difficulty in forming fine patterns because the copper used in plating through-holes enters the outer layers and adds to the thickness of copper deposit.
In recent years, strenuous efforts are being continued for the development of a multilayer printed circuit board having conductor layers and organic insulating films alternately built up or superposed on a substrate (build-up method) for the purpose of overcoming such problems as are attendant on the conventional method mentioned above. In this build-up method, such techniques as vacuum deposition and sputtering are generally adopted for the formation of conductor layers on insulating layers. The method, however, is at a disadvantage in betraying inferior productivity and entailing high cost.
In another method of producing a printed circuit board, a "fully additive" technique is employed. As one of the "fully additive" method, Japanese Patent Publication No. 4-6116 discloses a method which forms a conductor layer by electroless copper plating through the medium of an adhesive layer formed on an insulating substrate. In this method, an adhesive agent composed mainly of rubber, a filler, and a thermosetting resin is used for improving the adhesive force to be exhibited by a plating film to the adhesive layer. This adhesive agent is applied to the insulating substrate and allowed to harden thereon to produce the adhesive layer. Then, the adhesive layer is treated as with a mixture of chromate and sulfuric acid and cleansed with hot water to give rise to a surface construction in which the depressions formed in consequence of the removal of filler particles and the protrusions of rubber particles exposed in consequence of the removal of thermosetting resin are uniformly distributed. This method, however, is at a disadvantage in suffering the rubber component to persist within the adhesive layer and cause degradation of such properties as resistance to heat and electrical insulating properties.